(Adds detail, background)

ISLAMABAD, Jan 2 (Reuters) - Pakistani security forces have killed up to 25 al Qaeda-linked militants in fighting that began on Tuesday in the South Waziristan region on the Afghan border, the military said.

Many militants took refuge in South Waziristan and other parts of Pakistan's lawless tribal lands after U.S.-led troops toppled the Taliban regime in Afghanistan in 2001.

The militants have been making raids into Afghanistan and increasingly into Pakistan from remote mountain strongholds.

The government has accused a wanted militant leader based in South Waziristan, Baitullah Mehsud, of ordering the Dec. 27 assassination of opposition leader Benazir Bhutto in a gun and bomb attack in the city of Rawalpindi.

The latest clashes broke out in South Waziristan after militants kidnapped four paramilitary troops from a checkpost.

"We killed five miscreants yesterday and 15 to 20 in overnight fighting," military spokesman Major-General Waheed Arshad said on Wednesday.

At least 60 militants had been captured in the region since Tuesday, he said.

Tribal elders were trying to negotiate the release of the four abducted troops, he said.

Hundreds of people have been killed in clashes and suicide attacks in Pakistan in recent months, much of the violence taking place in the North West Frontier Province.

Arshad said he had no information about any operation to go after Mehsud, the militant commander accused of killing Bhutto.

A spokesman for Mehsud said the militant chief was not involved in Bhutto's murder. (Reporting by Kamran Haider; Editing by Robert Birsel and Roger Crabb)

AlertNet news is provided by